Normal cellular proliferation is initiated by growth factors which bind to their specific receptors to elicit a cascade of complex, intracellular signals that results in the sequential expression of genes important in regulating cell growth. Elucidating this genetic program will be essential for the understanding of both normal cell growth as well as the abnormalities in regulation that lead to cancer. This research proposal is directed at defining the role of a family of zinc finger-containing proteins as potential transcriptional regulators of the genes induced by growth factors in mammalian cells. The known members of this family include Zif268 (NGFI-a, Egr-1, Krox 24), Krox 20 (Egr-2), Egr-3, and WT- 1. Since members of this family (Zif268, Krox 20, WT1) bind specifically to a G/C-rich sequence in DNA, the family name G/C binding proteins (GCBPs) has been suggested. Zif268 and Krox 20, as well as several other known and putative transcription factors, are rapidly induced in mouse 3T3 fibroblastic cells by serum, PDGF, or FGF as part of the "immediate- early" genetic response to growth factors. Zif268 is also induced in pheochromocytoma (PC12) cells by NGF as an immediate-early gene. The next wave of expressed genes (delay-early genes) appears to be regulated by immediate-early transcription factors. In fact, the promoters of some delayed-early genes have been found recently to contain potential GCBP binding sites. Furthermore, a number of the immediate-early genes also have upstream potential GCBP binding sites. Thus, these genes are potential targets for regulation by GCBPs. To explore the possible role of GCBPs in regulating delayed-early genes, we plan to address the following questions: 1.) Do members of the GCBP family regulate delayed-early genes that have upstream GCBP sites? 2.) Do GCBPs act cooperatively with other immediate-early transcription factors to regulate target genes? 3.) If particular GCBPs regulate specific target genes, what domain(s) of the proteins confer the specificity? Our approach will be to test each of the delayed-early gene promoters with potential GCBP binding sites for response to each GCBP family member in transfection experiments, alone or with other immediate early transcription factors, where indicated. If we find evidence for cooperativity, we will look for interactions between transcription factors using a yeast genetic system designed for this purpose. If we find that certain GCBPs regulate specific genes differentially, we plan to make recombinant GCBPs to localize the specificity domains and use them to search for interacting proteins. Insight gained from these studies should advance our understanding of the role of GCBPs in regulating cell growth, and more generally, the reasons for having families of transcription factors that bind to the same DNA sequence.